Department of Engineering Science

EE442 Analog & Digital Communication Systems Spring 2017

Lecture 14

Cellular Telephones

References

• http://en.wikipedia.org/wiki/Wireless_network

• Preston Gralla, “How Wireless Works,” 2nd ed., Que Publishing, Indianapolis, IN, 2005.

• Wikipedia: http://en.wikipedia.org/wiki/History_of_mobile_phones

• V. H. MacDonald, “The Cellular Concept,” Bell System Technical Journal, Vol. 58,

January 1979

http://www.cellularconcepts.com/Home.html

Spring 2017 2

Advantages:

1. Convenience – User access from nearly any convenient location

2. Mobility (Portability) – User can maintain connection as they move around

3. Connectivity – Can receive signal where cables can’t go

4. Productivity – User can be connected almost 24/7

5. Deployment and Expandability – Easy to setup (plug ‘n play) & upgrade

6. Cost – Wide adoption means lower cost for installation and operation

Disadvantages:

1. Security – Signals readily intercepted and special efforts needed to add security

2. Range – Range limited by antenna power and landscape (scattering)

3. Reliability – Signal receptions depends upon many conditions and can’t be

guaranteed under all circumstances at all times

4. Speed – Generally data rates are lower than for wireline networks and more

users typically slows down the overall systems data rate performance

Wireless Networks – Advantages & Disadvantages

Spring 2017 3

https://www.inarratoronhold.com/blog/2015/10/6/evolution-of-the-telephone-part-2

1876

Alexander Graham Bell’s First Telephone

Spring 2017 4

The Evolution of the Telephone

http://deeperwonderment.wordpress.com/category/uncategorized/

Wired Telephone –

Started in 1876 with

switchboards & operators

Automated switching began in

the 1920s, but

PSTN reached full automation

only in 1980s (digital)

Wireless Mobile Telephone –

Voice only mobile phones

in early 1980s

Voice + data mobile phones

in 1990s

Mobile smartphones with the

Internet mid-2000s

Now everything is mobile!

Spring 2017 5

Two Parts of Cellular Telephone System

1. It is a radio (handsets are both transmitters and receivers)

2. It is a computer-controlled data communication network

Spring 2017 6

AT&T Mobile Radio Experiment in 1924

This mobile, two-way, voice-based phone was actually

more like a walkie-talkie than a telephone.

Antenna

Spring 2017 7

The First Mobile “Radio Telephone” System (1945)

The first mobile radio telephone system (AT&T) was developed and

inaugurated in the United States in St. Louis, Missouri, in 1945.

It consisted of six channels and did not work well due to interference.

A better idea was needed – the cellular telephone concept emerged!

It used a single high-power

base station which all use

to communicate.

PSTN Telephone

System

Its

coverage area

was called a

“small zone system”

Base

Station

Spring 2017 8

Cellular networks were developed to provide mobile telephony

Goal: telephone access “anytime and anywhere.”

AT&T’s idea was a mobile phone system involving the division

of the coverage area into "cells." These "cells" were intended

to reduce bandwidth interference and expand number of users.

Core Principles:

1. Small cells “tessellated” over entire coverage area

2. Must have call handoff as cell phones moved from one cell to

another cell

3. Incorporate “frequency reuse” over the entire cellular network to

increase number of users in network

AT&T’s Breakthrough Cellular Network Concept

handoff

1

2

3

4

Spring 2017 9

An Array of Cells Forms a Cellular Network

www.ece.lehigh.edu/~skishore/research/lucid/lucid_2.ppt

BTS Base Station

Transceiver System

A tessellation of small functional cells over the entire coverage area.

Definition: Tessellation is the process of creating a

two-dimensional pattern using the repetition of a

geometric shape with no overlaps and no gaps.

Cellular

Network

Spring 2017 10

Each BTS (Base Station Transceiver System) cell serves those users within the cell itself. Users located beyond the edge of the cell receive weak signals and are best served by adjacent cells.

Benefits: (1) Smaller cell size means that a lower power is required for Base

Transceiver Station and also for each cell phone (2) Greater number of customers can be accommodated with

frequency reuse

Single Cell in the Cellular Telephone Network

www.ece.lehigh.edu/~skishore/research/lucid/lucid_2.ppt

Cell phone

Cell phone

hexagonal shaped cell

BTS

Spring 2017 11

Perspective of the Cellular Service Provider vs. Its Customers

Spring 2017 12

HLR

VLR

EIR

AuC

MSC

BSC

BTS BTS BTS

MS

Air Interface

PSTN

ISDN

PSDN

MS MS

MS = mobile stations

MSC = mobile switching

center

VLR = visitor location register

HLR = home location register

AuC = authentication center

EIR = equipment identity

register

BTS = base transceiver

station

BSC = base station

controller

Keeping Track of Individual Users Within Network

PSTN = public

switched telephone

network

ISDN = integrated

services digital

network

PSDN = packet-

switched digital

network

Spring 2017 13

GSM (Groupe Speciale Mobile) Now known as “Global System for Mobile communication)

• GSM supports voice and circuit-switched data services (digital)

• GSM supports data rates up to 14.4 kbps

• Uses a SIM card to enable users to personalize services

• GSM channel is actually 271 kHz wide, but channels are spaced

at 200 kHz apart

• Considered to be a 2G (second generation) cellular system

• Two types of channels – control channels & traffic channels

• Frequency bands for GSM are shown in table below

GSM Band Uplink Frequency Band

GSM850

GSM/PCS1900

GSM900

GSM/DCS1800

824.2 to 849.2 MHz

1850.2 to 1909.8 MHz

880 to 915 MHz

1710.2 to 1784.8 MHz

Downlink Frequency Band

869.2 to 894.2 MHz

1930.2 to 1989.8 MHz

925 to 960 MHz

1805.2 to 1879.8 MHz

Spring 2017 14

GSM PLMN Architecture (Public Land Mobile Network)

NSS = Network Switching Subsystem

BSS = Base Station System

MSC = Mobile Switching Center

GMSC = Gateway Mobile Switching Center

BSC

BTS

BTS

BTS

BTS

BSC

BTS

BTS

BTS

BTS

Register

VLR

MSC GMSC

MSC

VLR

HLR AUC

EIR

Base

Station

Subsystem

Base

Station

Subsystem

BSS

BSS

Gateway

PSTN

PSDN

ISDN

BSS

BSS

NSS

Spring 2017 15

Efficient Use of Radio Spectrum Achieved By

Frequency Reuse – Repeats the use of the same frequencies by physically separating cells from each other

Dynamic channel assignment – One cell can borrow channels from an adjacent cell if that cell is under-utilized

Cell splitting – In high population density areas, cells can be made smaller to accommodate the greater number of users

(Note: Setup of “microcells” and “picocells”)

Cell sectoring – Use directional radio signals (typically cells are divided into three sectors per cell)

Offload to Wi-Fi – Allows Wi-Fi enabled cell phones use Wi-Fi hotspots which are connected to the cellular network

Spring 2017 16

A “cluster of 7” has six neighbors which forms the “reuse pattern.” The cellular network repeats this reuse pattern over and over. Using the same frequencies again in each “cluster of 7” allows a service provider to support many more cell phone users in the area.

Frequency Reuse in a Cellular Network

1

2

3

4

5

“Cluster of 7”

BTS Cells

BTS = Base Station Transceiver System

Spring 2017 17

Cell Splitting

Expanding the capacity of a

cellular system can be achieved

by increasing the number of cell

sites covering the entire

geography. With cells covering

smaller areas the reuse of the

same frequencies can be

applied more often within the

whole geographic coverage

area. Smaller cell sizes also

allows lower power operation.

Parameter Macrocell Microcell Picocell

Cell Radius 1 to 10 km 0.1 to 1 km < 0.1 km

Transmission Power 1 to 20 W 0.1 to 1 W < 0.2 W

Maximum Bit Rate 0.3 Mbps 1 Mbps > 1 Mbps

http://ironbark.bendigo.latrobe.e

du.au/subjects/DC/lectures/22/

Region of higher

population density

Region of lower

population density

Macrocell

Microcell

Picocell

Spring 2017 18

Principle:

An increase in network capacity can be

achieved by reducing the number of

interfering co‐channel cells. If sectoring is

done so that all channels assigned to a

particular sector are always it the same

direction in the other cells, then the

interference is reduced which allows the

cluster size to be reduced – that increases

the network’s capacity.

Cell Sectoring (Smart Antennas)

3-sector base station antenna

3-sector base station antenna

pattern can be optimized by

directing signal beams

(dynamic sectoring shown)

http://en.wikipedia.org/wiki/History_of_mobile_phones

Spring 2017 19

Artificial trees are commonly used to mount cellular antennas and even

saguaro cactus are used in desert areas.

References: http://aphotoathought.blogspot.com/2012/01/stealth-cellphone-towers.html and

http://www.mindfully.org/Technology/2003/Cell-Stealth-Antennas14jan03.htm.

Stealth Cellular Telephone Antennas

Spring 2017 20

Cellular Telephone Generations

1980 1990 2000 2010 2020

1G

Ca

pa

city E

nh

an

ce

me

nts

by G

en

era

tio

n

2G

3G

Voice Telephony

Analog Cellular

Digital voice, Data

and Messaging

Wideband Digital,

Enhanced Data &

Multimedia Services

Digital Voice, Data

and Multimedia, &

Very High Data Rates

4G

LTE

2.5G

Much higher

Data Rates

LTE is “Long

Term Evolution”

Outdated & Retired Today

“G” means generation

Spring 2017 21

Cellular Telephone Generation Summary

Generation

Technology

Network

Service

Data rate

Coverage

1G

Analog

Circuit-

Switched

Voice

Telephony

No Data

Limited

Coverage

2G

Digital

Circuit-

Switched

Voice &

Limited Data

(Narrowband)

Slow Data

Trans-

national &

Limited

Global

Roaming

2.5G

Digital

Circuit &

Packet-

Switched

Voice +

Higher Data

Rates

Fast Data

Global

Coverage &

Global

Roaming

3G

Digital

Circuit &

Packet-

Switched

Voice +

Advanced

Data (MM)

Faster Data

Global

Coverage &

Global

Roaming

4G

Digital

All IP Packet-

Switched

Voice &

Advanced

Multimedia

Even Faster

Global

Coverage &

Global

Roaming

Transition

Phase 3.5G

Spring 2017 22

http://en.wikipedia.org/wiki/Motorola_DynaTAC

Martin Cooper (31 years ago) designed

the Motorola DynaTAC 8000X

First Commercial Cell Phone: Motorola DynaTAC

Introduced by Motorola, it was …First Generation* (1G) “analog voice-only phone”

First sale in March 1983

Battery – 30 minutes of talk time & 8 hours of standby

Weighed ~ 2 pounds and 13 inches high (tall)

Stored up to 30 phone numbers; 10 hours to recharge

Price started at $3,995

The

“Brick”

* Known as AMPS for “Advanced

Mobile Phone System”

AMPS*

1G used

800 MHz &

900 MHz

radio bands

Spring 2017 23

Second Generation (2G) Mobile Phones

http://en.wikipedia.org/wiki/Global_System_for_Mobile_Communications

Second Generation (2G) introduced in early 1990s to replace 1G

Digital (rather than analog) transmission of voice

Designed for circuit-switched networks (voice centric)

Uses 900 MHz and 1800 MHz frequency bands

Dominant 2G phone standard: GSM (Global System for Mobile)

Introduced SMS (aka “text messaging”)

GSM uses SIM card containing user ID (Subscriber Identity Module)

Began in Europe; rapidly expanded around the World

http://sharingmythoughts-

ben.blogspot.com/2010/09/histor

y-of-mobile-phone.html

Nokia 2G

Mobile

Phones

GSM is still

widest used

cell phone

standard

Worldwide!

Spring 2017 24

• A small smart card (Subscriber Identity Module)

• Encryption codes needed to identify the subscriber

• Subscriber IMSI number (International Mobile Subscriber Identity)

• Subscriber’s own information (telephone directory)

• Third party applications (banking etc.)

• Can also be used in other systems besides GSM, e.g., some WLAN

access points accept SIM based user authentication

http://microsim-shop.com/making-

your-own-microsim.html

http://www.ricksteves.com/tm

s/article.cfm?id=166

MS = ME + SIM

GSM Introduced the SIM Card

Spring 2017 25

Third Generation (3G) Mobile Phones

Third Generation (3G) introduced in early 2000 s to upgrade 2G

Wider range of advanced mobile services & better quality of service

(e.g., delivers multimedia with broadband access to Internet)

Digital transmission using data packets

Uses both circuit-switched & packet-switched networks

Uses 1800 MHz, 1900 MHz and 2100 MHz frequency bands

Faster data rates:

144 kbps – wide area vehicular (rapid motion) environment

384 kbps – pedestrian or urban environment

2,000 kbps (2 Mbps) – stationary (e.g., within buildings) environment

http://www.cheap3gphones

.net/samsung-3g-phones/

Spring 2017 26

Fourth Generation (4G) Mobile Phones

Fourth Generation (4G) introduction began in 2011

Known broadly as LTE (Long Term Evolution)

Provides for much faster data rates

It is an all IP – uses only packet-switched networks

Uses 700 MHz, 1,700 MHz, and 2,100 MHz frequency bands

Greater than 100 Mbps data rates possible (with max 20 MHz channel)

Will take some years to fully implement

http://www.droid-life.com/2011/01/10/chart-verizon-4g-lte-android-

phone-lineup/

Verizon 4G LTE Android phones Droid Bionic, HTC Thunderbolt, LG Revolution, Samsung SCH-I510

Spring 2017 27

WLAN

Cellular

Gen

era

tion

Spring 2017 28

GSM

IS-95

CDMA

GPRS

CDMA2000

1x-RTT

EDGE

2G 2.5G 3G 3.5G 3.75G 4G

WCDMA

(UMTS)

CDMA2000

1x-RTT

HPSA

(UMTS)

LTE Advanced

LTE

Cellular Generations

Most Important Evolution of Mainstream Cellular

Spring 2017 29

Multi-X: Radios, Bands & Applications

• Cellular (3GPP: GSM/EDGE/ W-

CDMA/HSDPA/HSUPA);

450/800/800/1700/1900/2100 MHz

Cellular Diversity

• Audio

15 Radios 41 Bands 2M Apps

• FM Stereo

• A-GPS • DAB

WLAN

Diversity • WLAN • 802.11a/b/g

• Bluetooth

• Infrared

From John Harmon (11/2013)

DAB = digital audio broadcast;

The modern smartphone has multiple capabilities!

Spring 2017 30

Multi-band

Cellular Radio

Transceivers +

WiFi

High-speed

Processor

Unit

Interface

Electronics

Flash

Memory

Micro-

phone

Display

Speaker

Keypad

Alarms

Battery

Power

Management

External

Charger

Wi-Fi

Bluetooth

Screen

(display)

Radios Antenna

Antenna

Camera (2)

Organization of a Modern Cell Phone

Spring 2017 31

Challenges to Cellular: Multi-Path Propagation

Base

Transceiver

System (BTS)

Mobile Station (MS)

multi-path

propagation

Path Delay

Po

we

r

path-2

path-2

path-3

path-3

path-1

path-1

Your cell phone must contend with multiple signals to properly operate.

path -2

path -1 Note delay of path -2

Spring 2017 32

Multi-Path Fading

In communication systems, fading refers to a specific kind of

attenuation which is highly frequency and time dependent.

Other types of attenuation such as loss on transmission lines, path

loss in radio transmission, etc. do not change rapidly with time or

frequency, at least not within the bandwidth of interest.

On the other hand, multi-path fading varies strongly with time and

frequency and can - unlike other sources of attenuation - result in a

very large frequency-dependent attenuation. This is a result of

multi-path propagation.

Spring 2017 33

Small-scale fading – Exhibits rapid fluctuations of the amplitude,

phase or multipath delays of a radio signal over a short travel

distance or short time interval.

Large-scale fading – Results from signal attenuation from signal

Propagation over large distances and diffraction around large

Objects in the propagation path.

Small-Scale & Large-Scale Fading

Spring 2017 34

Types of Small-Scale Fading

Small-scale Fading (Based upon multipath time delay spread)

Flat fading 1. BW of signal < channel BW

2. Delay spread < Symbol period

Frequency Selective fading 1. BW of signal > channel BW

2. Delay spread > Symbol period

Small-scale Fading (Based upon Doppler spread)

Fast fading 1. High Doppler spread

2. Coherence time < Symbol period

3. Channel variations faster than

baseband signal variations

Slow fading 1. Low Doppler spread

2. Coherence time > Symbol period

3. Channel variations slower than

baseband signal variations

Spring 2017 35

Challenges to Cellular: Signal Attenuation

http://en.wikipedia.org/wiki/Terrestrial_Trunked_Radio

Radio signal strength becomes weaker as energy spreads out.

Cell 1 Cell 2

RSS = received signal strength

distance

Spring 2017 36

Additional Slides

(including cell phone

radiation effects)

Spring 2017 37

Electromagnetic Radiation Hazards

Mobile phone hazard

As of 2009 there were ~ 2.5 billion mobile phone users worldwide.

Mobile phones use EM radiation in the radio spectrum. There is

controversy about such emissions being harmful to human health.

Dr. Keith L. Black, a preeminent brain surgeon and author of the

book, Brain Surgeon: A Doctor's Inspiring Encounters with

Mortality and Miracles, 2009, has said,

“While some studies showed no correlation between cell phone use and

brain tumors, other credible studies show brain tumor incidence that is

250% greater than non-cell phone users.”

He recommends using a Bluetooth ear piece with your cell phone

to reduce radiation intensity around your head as a precaution.

Some cell phones emit approximately one watt of transmit power.

http://en.wikipedia.org/wiki/Electromagnetic_radiation_and_health

Spring 2017 38

EM radiation distributions in head @ 1900 MHz.

(a) 11 % larger head size, (b) average head size, and (c) smaller head

size (such as in a child – note proportionally larger heating).

Gandhi & Kang, Phys. Med. Biol., 47, 1501-18, 2002.

Head Models for Electromagnetic Energy Absorption

SAM (is “standard anthropomorphic mannequin”)

DECT 6.0 1900 MHz cordless phones

Large

Adult Child

Spring 2017 39

Some simple steps you can take to substantially reduce

exposure to cell phone radiation:

1. Use a wired headset or wireless Bluetooth headset, or use

phone in speaker-phone mode. Better yet, send text messages.

2. Keep cellphones away from your body (particularly

pant/trouser or shirt pockets) or use a belt holster designed to

shield your body. When not in use, put in it in “stand-by mode.”

3. Avoid using in a moving car, train, bus, or in areas with weak

reception – results in an increase in EM power by the cell phone.

4. Use the cellphone like an answering machine. Keep it off until

you want to see who has called. Then return calls you want to.

5. Do not allow children under 18 to use cellphones except in

emergencies or very limited circumstances.

How to reduce EM exposure in using cell phones